Investigations and Evidence
Core concepts
Investigations require both legal and practical competence. Candidates must know the chain of custody, evidence collection and packaging, crime scene security, and the rules governing identification procedures (show-ups, photo arrays, and lineups) with attention to suggestibility. Understand the hearsay rule and its major exceptions relevant to patrol officers, the best evidence rule, and the foundation required to authenticate physical and digital evidence. Know the elements of a lawful consent search - voluntariness, authority to consent, and scope - and how to document them. Understand how to write a search warrant affidavit: probable cause, particularity, and the nexus between the place to be searched and the items sought. Digital evidence requires special care: preservation letters, hash values, and chain of custody for devices.
Traps
Questions often test whether consent was voluntary when an officer implied the person had no choice. Another trap: a photo array where the suspect stands out (clothing, background, or the only photo of a certain race). Watch for chain-of-custody gaps - a break in custody can undermine admissibility even if the evidence is authentic.
Rule of thumb
For every item of evidence, answer: Who had it, where, when, and how do I prove it? If any link is missing, the chain is broken.
Worked example
An officer seizes a phone. Best practice: document the seizure, place it in airplane mode or a Faraday bag, log every transfer, and obtain a warrant specifying the data sought (messages, call logs) rather than the device generally.